Pan and ball mill



May 16, 1933. T. w. KEET PAN AND BALL MILL Filed Aug. 15, 1932 Patented May 16, 1933 UNITED STATES PATENT OFFICE;

THOMAS WILLIAM KEET, F JOHANNIESBURG, TEANSVAAL, UNION OF SOUTH .AFRICA PAN AND BALL MILL Application filed August 13, 1932, Serial No. 628,725, and in the Union of South Africa July 12, 1932.

The present invention relates to mills for fine grinding ores and other materials, of the kind comprising a circular panhaving anrinturned peripheral wall forming an annular trough, relatively around which a ball or a series thereof is caused to run; the pulp being introduced into such trough so that it is ground between the relatively moving ball or balls and the wall of the trough and is discharged over the lip of the trough.

According to the present invention, in a mill of the kind described, thepan is rotated about its own axis to cause the material to be retained centrifugally in the trough and thereby subjected to grinding by the balls until it is reduced to the desired extent; that is to say in the case of wet grinding, to, an extent which causesit tobe displaced-by the centrifugally acting larger particles, and, in the case of dry grinding, to an extent which permits its removal by air currents. The pan is gyrated to cause the balls to be propelled around the trough and thereby press centrifugally on the ore particles between them and the trough, the direction of their rotation being op osite to that or the pan; and a ball control ing arm is arranged to rotate around the trough in the wake of the balls to ensure that they do not lag and thereby cease to be propelled by the gyration of the pan. 7

The invention is illustrated in the accompanying drawing in which Fig. I is a sectional elevation of a mill suitable for wet grinding and comprising a plurality of troughs.

Fig. II is a plan of Fig. I.

Fig. III shows a modified construction which can be used for dry grinding.

2 indicates the pan which is circular and rigidly mounted on shaft 3 co-axial with it. Said shaft and pan are arranged to gyrate about a fixed axis 4. For this purpose in the example showm'the shaft 3 is formed at its lower end with'a ball 5 resting in a spherical step bearing 6. The upper end of the shaft is alsoformed with a ball 7 seated in a bearing block 8 eccentrically positioned'on a pulley 9 which is rotated in the fixed axis 4 by a belt 10. r

The bearing block 8 is adjustable radially 011 the pulley 9 in order to vary its eccentrioity. It is thus'adjusted by such means as a lever 11 pivoted at 12 to a fixed part and engaging a sleeve13 sliding on the shaft 14, the sleeve being connected to the block 8 by the link 15.

The pan is formed with a number of concentric troughs 16, 17, 18, 19, each of approximately half circular form in cross section so that balls can'roll around it and in do ing so crush material between them and it with the open side of the trough inward to retain the balls and material against centrifugal force. The troughs are provided with renewable wearing plates 21.

In the Fig. I arrangement the material is discharged from all the. inner troughsby flowing over the lip 22- of each into the succeeding trough, which is accordingly raised in order to receive such material. From the lip 23 of the final trough 19 the material passes into an annular receiver 24. from which it is withdrawn at 25. Thisarrangement is suitable for wet grinding. In the modified arrangement of Fig. III, some of the inner troughs such as 16 17 have holes 26 through which the material can pass into the next trough; the outer trough or troughs such as 18 19 being unperforated. This arrangement is better adapted for grinding fairly soft material or for dry grinding; and, for the latter, well known means for collecting the fine material by air currents is provided.

27 is an-arm which is fixed to the pulley 9 to rotate therewith. It may conveniently be steadied by being journalled on the shaft 3 and resting on a collar 28 thereon. It is desirable to provide a number of balls 20 in each trough,-and conveniently their number is such that they occupy an arc of about 90 degrees. Extending from the arm- 27 are subsidiary arms 29, one for each trough and positioned to be behind the series' of balls therein.

The shaft 3 is rotated about its own axis by means of a pulley 30 which may provide the foot step bearing 6 and which is driven by belt 31 so as to rotate oppositely to the pulley 9. An arm 32 fast on the shaft 3 has a downwardly depending end 33 slidable through a ball 34 carried in a spherical bearing 35. concentrically positioned in the pulley 30. 86 indicates a means for feeding the material to be ground, into the central area of the pan.

The operation is as follows: Rotation of the pulley 9 gyrates the pan 2 in the direction of arrow A, Fig. II, causing the balls 20 to run around the troughs in the same direction. The balls may tend to lag behind the gyration when the mill is being started-.orby reason of-excessive obstruction by the material under treatment,

and if such lagging were permitted, the balls could not be maintained in regular motion around the troughs. It is accordingly prevented by means of the arms 29 which follow in the wake of each series ofballs and drive, by positive contact, any'which fall behind. The balls are propelled around the troughs at a speed'high enough to cause them to exert substantially centrifugal force and so effectively crush material in the troughs. It is found convenient to set the bearing block 8 out at a considerable eccentricity when starting the mill and to reduce the eccentricity as the pulley 9 reaches its normal speed of rotation. i

The rotation of'the pan about its own axis throws the material centrifugally into the first'of the troughs and tends to retain it therein so that it is held in position to be effectively crushed between the ball and'the trough. As the rotation ofthe pan is opposite to that of the balls there is relative.

movement of the opposed crushing surfaces which causes the material in the troughs to be subjected to repeated crushing at frequent intervals. 1 i I V The centrifugal force tends to hold the coarser particles at thewidest parts of the troughs, where also the balls roll. As the particles becomesmaller they are less influenced by the centrifugal force and consequently flow over the lip 22 of the first trough into the second trough. There it is again subjected to crushing, and is in this way passed through the, several troughs in succession until its final discharge from the outermostlip 23. In the Fi III modificationfsome material passes directly through the holes 26 without passing over the lips of theperforated troughs. g

The width of he troughs and the diameter of the balls therein preferably decreasesprogressively towards the periphery, so that the material is subjected to successively finer grinding steps.

I claim: V 1. A mill comprising a circular pan provided with an annula ball-retaining trough, balls in the trough, means to gyrate the pan and thereby cause the balls torun around the trough, means rotating with the gyration in the wake of-the balls to'prevent their lagging behind the gyration, means to feed material to the inner area of the pan, and means to rotate the pan about its own axis oppositely to the direction of gyration and thereby subject the .material to centrifugal force. Y i

2.. A. mill comprising a circular pan formed with a series of concentric ball-retaining troughs, balls in the several troughs, means to gyrate the pan and thereby cause the balls to run around their troughs, an arm foreach trough rotating with the gyration and arranged in the wake of the balls in said trough, means to feed material to the pan area within the innermost trough, and means to rotate the pan about its own axis oppositely to the direction of gyration and thereby subject the material to centrifugal force, c

a 3. A mill comprising a circular pan formed with a series of concentric ball-retaining troughs each with an inwardly directed lip, each trough being elevated relatively to the next inner trough. to receive material centrifugally thrown from the lip of the latter, balls in'the several troughs, means to gyrate the pan and thereby cause the balls to run around their troughs, an arm for each trough rotating with the gyration and arranged in the wake of the balls in said trough, means to feed material to the pan area within the innermost trough, and means to rotate the pan about its own axis, oppositely to the direction of gyration and thereby subject the material to centrifugal force.

4. A mill comprising a circular pan provided with an annular ball-retaining trough, balls inthe trough, means to 'gyrate the pan comprising a shaft for the pan, a rotating member, a bearing block carried by said rotating member and supporting the shaft, and means to adjust the bearing block radially on the rotating member, an arm fixed to said member to rotate therewith and extending into' the trough in the wake of the balls therein, means tofeed material tothe inner area of the pan, and means to rotate the pan on its own axis oppositely to the direction of gyration and thereby subject the material to centrifugal force.

5. A mill comprising a circular pan formed with concentric ball-retaining troughing, outer troughing being unperforated and providedwith an inward material-containing lip and inner troughing being perforated, balls in the troughing, means to gyrate the pan and thereby cause the balls to run around'thetroughing, means driven bythe pan gyrating means and travelling around the troughing in the wake of the balls therein, means to feed material to the pan area Within the innermost troughing, and means to rotate the pan about its oWn axis oppositely t0 the direction of gymtion and thereby subject the material to centrifugal force.

In testimony whereof I aflix my signature.

THOMAS WILLIAM KEET. 

